Neurons and Neurotransmitters

As you may already know, the word “neuron” is a label for specialized cells in your brain and nervous system (and in your heart as well, for that matter) that have a highly developed ability to exchange information with each other. Most humans call that “thinking. Estimates are that you have 100 billion neurons in your brain, give or take a few billion. Some even say you have more neurons than there are stars in our galaxy!

Imagine your hand is a neuron. The palm of your hand represents the cell body (or face, if you will). Your thumb represents the axon or largest projection. Think of it as the door out of the neuron.

Your fingers represent dendrites, smaller projections whose job is to collect information and bring it inside the cell so it can be processed (e.g., you can think about it).

In order for you to think, neurons have to exchange information with each other, but they don’t actually physically touch each other to do this. One of the ways in which they exchange information is by means of a synapse.

A bit of chemical information is released from the terminal at the end of an axon. This chemical information is picked up by tiny boats (neurotransmitters) if you will, and ferried across the tiny canal (synaptic gap). On the other side of the canal it is picked up by the dendrite of another neuron. The tiny boats return to dock at the axon terminal, ready to be used again as needed.

The communication possibilities are virtually unlimited! Researchers have estimated that there may be more synaptic connections in your brain than there are atoms in our universe! How’s that for potential?

Use it or lose it!

Neurons function much in the same way as muscle tissue. Neurons tend to get stronger with mental exercise. In fact, the more they are challenged and stimulated the stronger they become and the further they stretch. This shortens the distance across the synaptic gap (or canal). Of course the reverse is true. Neurons tend to shrivel up and atrophy with disuse. This can be the basis for some age-related memory problems or other “thinking” dysfunction. Some of these problems can even be reversed for a time with increased brain stimulation.

Acetylcholine is produced and used all over the brain (unless other neurotransmitters such as dopamine that a produced in specific brainstem nuclei). Deficiencies are associated with memory loss and can eventually impair all cognitive brain functions. When levels are low the ability to boot up the mind is diminished. (Guiffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. p 30-32. NJ: Career Press, 1999.)

A electric signal known as the action potential is generated within the body of the neuron. It travels along the axon until it reaches the terminal. Between it and the next neuron is a gap called a synapse. (Goldberg, Elkhonon. The Executive Brain. p 28. NY: Oxford University Press. 2001.)

The brain has its own set of immune cells, called microglia, which can secrete C1q, a protein that has been implicated in diseases such as Alzheimer’s and Parkinson’s. This protein appears to lodge in synapses (the point between neurons) and is associated with cell death when a brain injury occurs. Levels of C1q appear to increase with age. According to professor and chair of neurobiology and senior author of the study, Ben Barres MD, PhD: “The first regions of the brain to show a dramatic increase in C1q are places like the hippocampus and substantia nigra, the precise brain regions most vulnerable to neurodegenerative diseases like Alzheimer’s and Parkinson’s disease, respectively.” Children don’t get Alzheimer’s and Parkinson’s and these findings may help to explain that phenomenon. (Source)

Neurons, thinking cells, are generated in the mature mammalian layer of the human brain, in the hippocampus, every day. However, their production is influenced by a number of different environmental factors. For example, the consumption of alcohol has been shown to retard the generation of new neurons. (Shors, Tracey J. “Saving New Bain Cells.” Scientific American, p 47-48, March 2009)

Neurons are the most fundamental signaling units of the human nervous system. They gather information about the brain’s internal state and the body’s external environment, analyze the data, and respond by coordinating appropriate actions. Typically, neurons consists of:

Cell body or soma (metabolic center and primary site of neuronal protein synthesis)

Dendrites (the primary conduits for receiving information from other neurons)

Axons (may be more than 3 feet long and emit neurotransmitters that transport messages from one cell to another)

Presynaptic terminals (numerous delicate swellings at the end of an axon that end at a synapse)

Oxygen generates the energy that fuels cells and, in the process, releases free radicals (molecules that are missing an electron). Antioxidants help to defend against free radicals. Glutathione, one of the most powerful antioxidants in the body, is packed in highest concentration inside glia, specifically astrocytes. Thus, astrocytes can survive toxins that can produce high enough levels of reactive oxygen to kill neurons instantly. Astrocytes release antioxidants in an attempt to protect neurons that are under the threat of oxidation. (Fields, R. Douglas, PhD. The Other Brain. p 104-106. NY: Simon & Schuster, 2009.)

The brain undergoes extensive remodeling as it moves through adolescence, resembling a network and wiring upgrade. For starters, the brain's axons—the long nerve fibers that neurons use to send signals to other neurons—become gradually more insulated with a fatty substance called myelin (the brain's white matter), eventually boosting the axons' transmission speed up to a hundred times. [http://ngm.nationalgeographic.com/print/2011/10/teenage-brains/dobbs-text]

Axons (nerve fibers) are output channels and dendrites are input channels. The end of the axon, the terminal, branches many times before it ends, allowing a single neuron to spawn many terminals. The axon most often forms connections with dendrites, but can also contact cell bodies or other axons. (LeDoux, Joseph.Synaptic Self. p 40-42. NY: Penguin Books, 2002.)

Axons (nerve fibers) are output channels and dendrites are input channels. The end of the axon, the terminal, branches many times before it ends, allowing a single neuron to spawn many terminals. The axon most often forms connections with dendrites, but can also contact cell bodies or other axons. (LeDoux, Joseph.Synaptic Self. p 40-42. NY: Penguin Books, 2002.)

The axons have two essential functions: to transport chemical substances, and to conduct information in the form of electrical stimulation. (Jensen, Eric. Brain-Based Learning (Revised). p 28. CA: The Brain Store, 2005.)

Some neurons have no axons or very short ones; others have axons almost as long as the person is tall (e.g., lowest part of the brain to the toes). (Tortora, Gerard J., and Sandra R. Grabowski. Principles of Anatomy and Physiology, 10th Edition. p 390. NY: John Wiley & Sons, Inc., 2003.)

Axons, the largest projection from a nueron, can be 3 feet long, but dendrites are always short—less than a millimeter. (Brynie, Faith Hickman. 101 Questions Your Brain Has Asked About Itself But Couldn’t Answer, Until Now. p 11, 32, 41. CT: Millbrook Press, 1998.)

Myelinated axons in the human brain are as small as one-thousandth of a millimeter in diameter. Not all axons are myelinated: only those that must carry information at high speeds and over long distances. (Fields, R. Douglas, PhD. The Other Brain. p 40-41. NY: Simon & Schuster, 2009.)

Axons are the brain’s equivalent of wires. The thin threads are each only 1 hundredth of the thickness of a human hair. (Katz, Lawrence C., PhD and Manning Rubin. Keep Your Brain Alive. p 11.NY: Workman Publishing Company, Inc., 1999.)

An adult human brain contains well over 100,000 miles of axons and countless dendrites, estimated to be sufficient to wrap around the earth over four times. (Tanzi, Rudolph E., PhD, and Deepak Chopra, MD. Super Brain. p 21. NY: Random House Inc., 2012)

Calcium is the main currency of information inside all cells, including neurons, the primary means to transmit information from outside the cell into the interior cytoplasm. Cellular membrane pumps, much like those holding back the sea in a levee system, constantly pump calcium out of the cell so that there is 10 million times less calcium inside the cell than outside. (Fields, R. Douglas, PhD. The Other Brain. p 49-50. NY: Simon & Schuster, 2009.)

Mature neurons don’t undergo cell division so rarely become cancerous (e.g., cancer is a failure of brakes that stop cellular division thus leading to runaway growth of cells into tumors). Neuroblastomas do occur although they are not common. They usually arise in the first three years of life and are rarely seen in adults. (Fields, R. Douglas, PhD. The Other Brain. p 69-70. NY: Simon & Schuster, 2009.)

Each neuron has its own cellular battery for energy. Glial cells (astrocytes) recharge the battery and help control the power source for neurons by controlling charged ions outside the neuron (e.g., there is an excess of negative charges inside the cell membrane giving the nerve cell a voltage of -0.1 volt. (Fields, R. Douglas, PhD. The Other Brain. p 45-46. NY: Simon & Schuster, 2009.)

The operations of individual cells are molded primarily by its interaction with the environment, not by its genetic code. The Science of Epigenetics (cellular memory) involves the study of the molecular mechanisms by which environment controls gene activity. (Lipton, Bruce, PhD. The Biology of Belief. p 85-86. CA: Mountain of Love / Elite Books, 2005.)

Neurons begin to die soon after their axons are severed, even though their cell bodies may be located far away from the site of injury. When axons are severed, genes in the neurons activate to cause them to self-destruct, a form of cellular suicide. Axons in the peripheral nervous system may be able to repair themselves, but axons in the brain and spinal cord appear incapable of doing so. (Fields, R. Douglas, PhD. The Other Brain. p 85-87. NY: Simon & Schuster, 2009.)

The CNS is made up of the brain and spinal cord. They are comprised of neurons and support cells that help keep up with the high maintenance and metabolic (glucose and oxygen) demands of the specialized nerve cells. (Guiffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. p 18-20. NJ: Career Press, 1999.)

Also known as Hereditary Motor and Sensory Neuropathy (HMSN), this peripheral neuropathy affects motor and sensory nerves outside the Central Nervous System. It is one of the most common inherited neurological disorders. Symptoms may include foot and lower-leg weakness, and atrophy of hand muscles. (National Institute of Neurological Disorders and Stroke. NINDS Charcot-Marie-Tooth Disease Fact Sheet. Accessed 2007.)

The composition of neurotransmitters and the functional biochemistry of the receptors are changing all the time. Some of that change is dependent on what you eat and what you do. Choline, for example, the precursor for acetylcholine, is readily found in egg yoke. (Carper, Jean. Your Miracle Brain. p 11. NY: HarperCollins Publishers, Inc., 2000.)

The combined circuitry that links together all the neurons of the cerebral cortex totals on the order of several hundred thousand miles. All this connectivity exists within a thickness of 1.5 – 4.5 mm. (Restak, Richard. Mysteries of the Mind. p 11-12. Washington, DC: National Geographic: 2000.)

Neurons may represent the most diverse type of cell in the body. Within the three classes of neurons are hundreds of different types, each with specific message-carrying abilities. The way in which these neurons communicate with each other by making connections is what makes each of us unique in how we think, and feel, and act.

Sensory neurons carry information from the sense organs (such as the eyes and ears) to the brain.

Motor neurons have long axons and carry information from the central nervous system to the muscles and glands of the body.

University of Sydney Studies: Syndapin, a key protein and molecular partner of another protein named dynamin, has been identified. The relationship between these two proteins has implications for increased understanding of other processes such as vision, forming memories, and during learning when there is a high level of brain activity and nerve transmission. (ScienceAlert; Australia and New Zealand. Brain Cell Communications. June 2006.)

The full sequence of communication between neurons is usually electrical-chemical-electrical: electric signals coming down axons get converted into chemical messages that help trigger electrical signals in the next cell. (LeDoux, Joseph. Synaptic Self. p 47. NY: Penguin Books, 2002.)

Researchers at Northwestern University have recently discovered information about how neurons work that is contrary to what is in neuroscience textbooks, such as:

Axons can operate in reverse, sending information to the cell body (and not just away from it)

Axons can talk to each other without any involvement with the cell body or dendrites

A neuron can store and integrate stimuli over a long period of time, from tens of seconds to minutes

Each cell in the brain can be compared to a separate computer. Substances called neuropeptides appear to form an electrochemical communications web that helps all the cells work in unison. (Perricone, Nicholas, MD. The Perricone Promise. p 6-7. NY: Warner Books, 2004.)

In your nervous system, information is handed from one nerve cell to another through two arms, called dendrites and axons, stretching out from opposite sides of each cell. The axon carries information away from a nerve cell, or neuron, and passes it to the dendrite of another; dendrites receive the information, which travels through the cell to the axon. The region where information is transferred from one neuron to another (and where axons and dendrites connect with each other) is called the synapse. Scientists are trying to draw a complete atlas of these connections (connectome) to gain a better understanding of how the brain functions in health and disease such as autism, schizophrenia, and perhaps Alzheimer's. (Study shows map of brain connectivity changes during development.)

Studies: Alterations of norepinephrine and other neurotransmitters may affect the creative process. The minds of exceptionally creative people may be capable of regulating norepinephrine – to decrease levels during periods of creative innovation and pave the way for discovery of unanticipated associations. High levels of norepinephrine constrict the diversity of available concepts; low levels have the opposite effect. (Heilman, K. M. Creative Innovation: Possible Brain Mechanisms. 9(5):369-379. Neurocase. 2003.)

Each neuron is a distinct cell separate from every other neuron. Neurons send signals along axons. A tiny gap separates the ends of axons from dendrites, the receiving ends of neurons. Human neurons have on average 10,000 synapses. In the mouse brain, every neuron made nearly all its connections with just one other neuron. (Zimmer, Carl. “Secrets of the Brain.” P 34-45, National Geographic, February 2014. Washington DC: National Geographic Society.)

Any intellectually challenging activity stimulates dendritic growth, which adds to the neural connections in the brain. (Ratey, John J., MD. A User’s Guide to the Brain. p 43. NY: Vintage Books, 2002.)

Tiny hair-like filaments that project from the neuron (the word dendrite comes from the Greek word for tree). Brain cells never actually touché physically, just reach toward each other with dendrites across a gap or synapse. (Chopra, Deepak, MD. Ageless Body, Timeless Mind. p 23-25. NY: Harmony Books, 1993.)

The brain has over 100 billion neurons, each having 10,000 or more dendrites that connect with other neuronal structures. (Newberg, Andrew, MD., and Mark Robert Waldman. Why We Believe What We Believe. p 17-18. NY: Free Press, 2006.)

Dendritic spines are tiny compartments that protrude from the dendrites of neurons that “receive” inputs from most excitatory synapses in the brain. Dendritic spines grow during normal maturation of the brain but are lost or abnormal in shape in many human neurological diseases, including mental retardation and dementia. Dendritic spines are mobile (e.g., they change their number and shape in response to the brain’s experience and to electrical signaling in the brain). (Sheng, Dr. Morgan. Brain Science Institute. Dendritic Spines - Tiny Structures in the Brain for Communication and Information Storage. May 2005.)

The process by which neurons differentiate to their specific functions begins at approximately 14 weeks of gestation and continues through the first year of life. (Karr-Morse, Robin, and Meredith S. Wiley. Ghosts from the Nursery. p 52-53. NY:Atlantic Monthly Press, 1997.)

Neurons differentiate to perform distinct functions, first by traveling to a specific site, and then by helping neighboring neurons make connections and develop colonies. Accurate migration can mean the difference between normal and abnormal functions. (Ratey, John J., MD. A User’s Guide to the Brain. p 23. NY: Vintage Books, 2002.)

Some diseases of the brain are the result of the unnatural deaths of neurons. Following are five examples:

Alzheimer’s disease, unusual proteins build up in and around neurons in the neocortex and hippocampus, parts of the brain that control memory. When these neurons die, people lose their capacity to remember and their ability to do everyday tasks. Physical damage to the brain and other parts of the central nervous system can also kill or disable neurons.

Blows to the brain, or the damage caused by a stroke, can kill neurons outright or slowly starve them of the oxygen and nutrients they need to survive.

Huntington’s disease, a genetic mutation causes over-production of a neurotransmitter called glutamate, which kills neurons in the basal ganglia. As a result, people twist and writhe uncontrollably.

Parkinson’s disease, neurons that produce the neurotransmitter dopamine die off in the basal ganglia, an area of the brain that controls body movements. The brain can no longer control the body and people shake and jerk in spasms.

Spinal cord injury can disrupt communication between the brain and muscles when neurons lose their connection to axons located below the site of injury. These neurons may still live, but they lose their ability to communicate.

Neurons are not all alike in the way they look or function. In fact, they differ from one another more than cells in any other organ. Some neurons send electrical signals along fibers that stretch several feet; other neurons’ branches extend only a few millimeters from the cell body. Some neurons possess a fractal beauty similar to that of ferns and corals (e.g., Purkinje cells may sport finely branched nets, like a sea fan). But some of their neighbors look more like tangled tumbleweeds. One neuron might appear more or less round under the microscope—like a firework frozen in climax—whereas another might spider through the brain like a daddy longlegs. The brain is a multi-diverse and inclusive universe. (Source)

Nearly all drugs of abuse act in a similar way in the brain’s reward system (e.g., areas that respond to stimuli such as food and drink and drugs). The drugs stimulate brain cells to release dopamine. (Research Report, Marijuana Abuse.National Institute on Drug Abuse, US Department of Health and Human Services, National Institutes of Health. NCADI NIDA)

Dopamine is produced in the brain stem and is pumped to other brain regions. It generates motivation to win designated rewards. If the expected reward is delayed, dopamine levels increase. High levels of dopamine are associated with anxiety, fear, intense motivation, and goal-directed behaviors. (Fisher, Helen.Why We Love. p 160-165. NY: Henry Holt and Company, 2004.)

Study: Much of what is known about rewards centers around the role of dopamine, produced by cells located in the ventral tegmental area of the brain stem (axons reach the prefrontal cortex and release dopamine). This chemical is a critical factor in the reward process (although there are rewarding conditions that do not depend on dopamine). (LeDoux, Joseph. Synaptic Self. p 188-189, 245-247. NY: Penguin Books, 2002.)

Two studies have linked ADHD with a deficiency in dopamine in the brain. This may be one reason for higher risk for substance abuse in people with ADHD as they attempt to self-medicate their brains. (Amen, Daniel, MD. The Brain in the News, Amen Clinic Newsletter. August, 2007.)

Dopamine, the feel-good chemical, may not be the reward in and of itself. Rather, it may produce a “go” signal that produces an action, which becomes the reward. (Zull, James, E., PhD. The Art of Changing the Brain. p 60-61. Virginia: Stylus Publishing, LLC, 2002.)

Dopamine helps to alert the mind that something important is about to happen. It stimulates pleasurable feelings. This helps to explain the long-lasting hold that addictive behaviors can have. (Zickler, Patrick. Addictive Drugs and Stress. p 1, 6-7. MD: National Institute on Drug Abuse, NIDA NOTES, Vol 18, No 5, Dec 2003.)

Elevated levels of dopamine in the brain can result in a variety of characteristics including persistence, unwavering motivation, ecstasy, and an increase in testosterone levels that can trigger sexual desire. (Fisher, Helen, PhD. Why We Love. p 52-60, 82-83. NY: Henry Holt and Company, 2004.)

All addictive drugs trigger the brain into producing a normal level of dopamine. (Bragdon, Allen D., and David Gamon, PhD. Brains that Work a Little Bit Differently. p 30-31. NY: Barnes and Noble Books, 2000.)

Studies of biological basis of desire to take drugs: fluctuations in dopamine (brain chemical) levels in the nucleus accumbens. This can occur by drugs itself or by an encounter with someone/something associated with past drug-taking. (Zickler, Patrick. Acute Dopamine Surge May Erode Resolve to Abstain. MD: National Institute on Drug Abuse, NIDA NOTES, Vol 19, No 1, p 1, 6. April, 2004.)

Serotonin and Dopamine must be constantly rebalanced in the brain. Stress can negatively impact this balance. When the rebalancing efficiency is impacted seriously, the chemical balance become severe enough to begin to see symptoms (e.g., depression). (Bost, Brent W., MD, FACOG. Hurried Woman Syndrome. p 14-15. NY: Vantage Press, 2001.)

Dopamine is manufactured in the body from tyrosine. Dopamine can sexually stimulate males but apparently not females. (Durden-Smith, Jo, and Diane deSimone. Sex and the Brain. p 254-260. NY: Arbor House Publishing, 1983.)

Dopamine is a neurotransmitter essential for alert awareness. It seems to be involved with excitement felt from novel stimuli and most responsible for the initial excitement that comes with the use of cocaine, amphetamines, alcohol, and with addictive behaviors. (Guiffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. p 31-32. NJ: Career Press, 1999.)

Two names for similar substances (endorphin label assigned by American researchers, enkephalin label assigned by Scottish researchers). Believed to be the body’s own natural opiate, consists of a pair of peptides, each five amino acids in length. (Pert, Candace, PhD. Molecules of Emotion. p 67. NY: Scribner, 1997.)

Endorphins, the body’s own morphine, are now identified as a subcategory of neuropeptides (substances that impact mood). (Perricone, Nicholas, MD. The Perricone Promise. p 6-10. NY: Warner Books, 2004.)

Endorphins are internal chemicals associated with the sensation of being “in love.” They help to strengthen the immune system. (Pease, Barbara and Allan.Why Men Don’t Listen and Women Can’t Read Maps. p 156-157. NY: Broadway Books, 1998.)

Endorphins are neurochemicals that contribute to a positive mood. Their production is stimulated by physical exercise (refer to Exercise and the Brain). (Hartmann, Thom. The Edison Gene. p 129-130. VT: Park Street Press, 2003.)

Large numbers of neurons are contained in the enteric nervous system, about 200-600 million in humans; similar to the number of neurons in the spinal cord and far more neurons than occurs in any other peripheral organ. Two-way communication occurs between the enteric nervous system and the immune system of the gastrointestinal tract, that is, transmitters released by the terminals of enteric neurons in the mucosa influence immune-related cells, such as mast cells, and the cells of the mucosa release active substances, including cytokines and mast cell tryptase, that act on enteric neurons. [John B. Furness. Scholarpedia, 2(10):4064]

Studies have shown that rats that exercise regularly can produce twice as many new cells in the hippocampus than those who lead a more sedentary lifestyle. However, unless the rats are cognitively challenged, the new neurons disappear rather quickly and do not survive indefinitely. (Shors, Tracey J. “Saving New Bain Cells.” Scientific American, p 47-48, March 2009)

Studies have shown that rats that exercise regularly can produce twice as many new cells in the hippocampus than those who lead a more sedentary lifestyle. However, unless the rats are cognitively challenged, the new neurons disappear rather quickly and do not survive indefinitely. (Shors, Tracey J. “Saving New Bain Cells.” Scientific American, p 47-48, March 2009)

Johns Hopkins University scientist study: Growing fat cells and nerve cells in the same dish has produced what is believed to be the first demonstration of two-way communication between the cell types. The study, using rat and mouse cells, provides the first clear evidence that signals from fat cells can directly influence neurons outside of the brain. Researchers believe this has implications for understanding the storage and burning of fat, obesity, and related disorders, such as diabetes. (Source)

In the fetus, glial cells form the scaffolding that regulates the survival and differentiation of neurons. Glial cells allow the rest of the nervous system to develop. (Jessen, Kristjan R. Cells in Focus: Glial Cells. Int J Biochem Cell Biology. 36:1861-1867, 2004.)

The cortex constitutes nearly 70% of the nervous system. Its neurons are connected by nearly one million miles of nerve fibers. (Jensen, Eric. Brain-Based Learning (Revised). p 26. CA: The Brain Store, 2005.)

Studies at the Max Planck Institute for Dynamics and Self-Organization: Information stored in the activity patterns of cerebral cortex neurons is discarded at the surprisingly high rate of one bit per active neuron per second. The dynamics of the cerebral cortex are specifically tailored to the processing of brief snapshots of the outside world. The Göttingen-based researchers were able to calculate, for the first time, how quickly an activity pattern is lost through tiny changes; in other words, how it is forgotten. No wonder "practice makes perfect," and learning requires repetition. (Ref.: Physical Review Letters, 105, 268104, 2010).

The frontal lobes have vastly fewer neurons than the number in the visual areas, the other sensory areas, and the motor areas of the cortex. What is larger in the frontal lobes than the rest of the brain, is the arborization of the neurons, the branching of the dendritic tips with the resulting possibility of increased connections. (Gazzaniga, Michael S. Who's In Charge? p 30-32. NY: HarperCollins Publishers, 2009)

Mouse research (published in The Journal of Neuroscience) has shown that the lower digestive tract in adults can be stimulated to produce new neurons in the intestinal system. Estimates are that the enteric nervous system contains a million neurons (that control the gastrointestinal or GI system), half of all the dopamine in your brain and body, and perhaps ninety percent of all serotonin. No wonder what is going on in your brain can be acted out in GI symptoms! The research showed that drugs similar to serotonin increased the production of new neurons in the intestinal walls. (Source)

A big part of your emotions are probably influenced by the neurons, neurotransmitters, other chemicals, and nerves in your gastrointestinal system. Serotonin, for example. Estimates are that about 95% of your body’s Serotonin is found in the gastrointestinal system or gut. Serotonin is an extremely important neurotransmitter, a well-known contributor towards feelings of well being. Sometimes it is also called a “happiness hormone”. (Hadhazy, Adam. Think Twice: How the Gut’s “Second Brain” Influences Mood and Well Being. Scientific American, February 12, 2010)

Glial cells have sensors that can detect a large number of neuronal signaling molecules, including all the various neurotransmitters neurons use for synaptic communication. Glial cells monitor neuronal communications. (Fields, R. Douglas, PhD. The Other Brain. p 57-58. NY: Simon & Schuster, 2009.)

Glia means glue in Greek. Glial cells outnumber neurons by at least 10 to 1. They are now believed capable of encoding and transmitting information on their own. The number of elements involved in information transfer, along with their interactions, represents a number likely greater then the number of particles in the known universe. (Restak, Richard. Mysteries of the Mind. p 11-12. Washington, DC: National Geographic, 2000.)

French National Centre for Scientific Research studies: glial cells, formerly believed to be just supports for neurons, release molecules that bind to neuronal receptors and facilitate the transmission of information. (Glial cells: essential to brain communication, 2006.)

The brain consumes the equivalent of a quarter pound of glucose every day, more than any other body organ except for muscles during heavy exercise. The bulk of the energy is used to make neurotransmitters. (Treadwell, Benjamin V., PhD. The Brain: Can We Tweak it? CA:Juvenon Health Journal, Vol 4, No. 4, p 12. April 2005.)

The heart has its own independent nervous system with at least 40,000 neurons (as many as are found in various subcortical sections of the brain). There is a 2-way nervous system relay between the brain and the heart. (Childre, Doc and Howard Martin. The HeartMath Solution. p 10, 23. CA: Harper SF, 1999.)

Did you know that in addition to electrical signaling, the heart releases peptides that can impact your mood? Think of the heart as an endocrine gland. The peptides it releases help in blood pressure modulation and improving the functioning of kidneys. These peptides also stimulate the pituitary gland thereby helping it to release hormones like oxytocin commonly referred to as “love” or bonding hormone. Oxytocin also helps in increasing a sense of wellbeing. This could be a basis for saying that happy feelings emanate from the heart. (Cartin, M., and J. Genest. “The Heart as an Endocrine Gland,” Scientific American, February 1986, Vol. 254, No. 2, p 62-67)

Did you know your heart maintains a sophisticated circuitry of neurons, neurotransmitters, proteins and support cells that qualify it as an intelligent brain? The heart is constantly involved with processes throughout the body, whether it is pumping blood through your system, communicating with cells or sending out strong rhythmic signals to the cranial brain that dramatically affect thinking, perception and performance. Achieving an optimal state depends on the synchronicity/harmony of bodily systems including maintaining what is known as a coherent heart, one that is marked by smooth rhythms, helps a great deal. The coherent heart sends out coherent signals to the brain and the rest of the body, thus promoting system-wide harmony. (Source)

The heart is filled with neurons. This relatively new area on ongoing research is releasing study results almost weekly. The Institute of Heart Math has now published photographs of neurons in the heart--some taken with a confocal microscope. Researchers call these neurons "the little brain in the heart." (Source)

Andrew Armour MD, PhD, a neurologist from Montreal, Canada, discovered a small but complex network of neurons in the heart, which he has dubbed ‘the little brain in the heart’. These neurons seem to be capable of both short and long term memory.... There is a lot of communication that occurs between the heart and the brain. There are 40,000 neurons in the heart which communicate with the brain. (Bridger, Darren. Can your heart think and feel?2006.)

According to Attilio, neurocardiologists have found that 60-65% of the cells of the heart are actually neural cells (not muscle cells as was previously believed). Identical to neural cells in the brain, they operate through ganglia and with the same axonal and dendritic connections, as well as through the very same types of neurotransmitters. (D’ Alberto, Attilio, BSc (Hons). Cellular Memory and ZangFu Theory.)

The axons of some neurons are wrapped with electrical insulation called myelin. That allows electrical impulses to travel across the wire-like axons as speeds of up to 200 miles per hour. (See Pain for speed of transmission across non-myelinated axons.) (Fields, R. Douglas, PhD. The Other Brain. p 19. NY: Simon & Schuster, 2009.)

Histamine originates in cells near the hypothalamus. Histamine helps to increase brain metabolism, making it easier to concentrate. That’s one reason antihistamines, such as Benadryl, that block histamine’s actions can cause sleepiness and make it difficult to stay attentive and to focus. (Guiffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. p 30-32. NJ: Career Press, 1999.)

Mirror neurons play a key role in sexual response and may play a role in homophobia. When people see sexually aroused genitals of thepreferred sex (e.g., opposite for heterosexuals, same for homosexuals), the brain's mirror neurons and reward centers fire. So when a heterosexual male sees two other men in sexual acts, he can't help but experience it in his mind's body, even if it is at a subconscious level. For the straight male, this is unappetizing and may make a live-and-let-live attitude more difficult to adopt. (Blakeslee, Sandra, and Matthew Blakeslee. The Body Has a Mind of Its Own. p 178-179. NY: Random House, 2008.)

Specific neurons appear to be involved in holistic thinking. Holistic functions are not language based, however, and so are more difficult to define or communicate. The right hemisphere appears to carry out primarily holistic thinking. The human brain is capable of both holistic and reductionist thinking but not at the same time. (Newberg, Andrew, MD and Mark Robert Waldman. Why We Believe What We Believe. P 90-95. NY: Free Press, 2006)

Dr. Daniel Siegel is the founder of interpersonal neurobiology, a new field that studies the "social brain." It includes a multitude of circuitry designed to interact with another person's brain. One key discovery was "mirror neurons They activatge in you exactly wha you see in another person including emotions, movements, and even intentions. (Goleman, Daniel Jay, PhD. The Brain and Emotional Intelligence: New Insights. p 54-58. MA: More Than Sound, 2011)

Krabbe disease is a rare, incurable genetic disorder caused by a deficiency of an enzyme that is necessary for myelin metabolism. This can cause deterioration of the myelin sheath and death of brain cells. It affects both the central and peripheral nervous systems. Symptoms may appear during the first six months of life, during adolescence, or adulthood. (National Institute of Neurological Disorders and Stroke. NINDS Krabbe Disease Information Page. Accessed 2007.)

The word neuron, as we understand it today, did not exist before 1891. In that year, German anatomist Wilhelm Waldeyer dubbed the discrete cells that form the nervous system neurons. (In 1896, Rudolph Albert von Kolliker coined the termaxon to describe the long slender cables that transmit signals away from cell bodies. In 1889, William His named the thin branching fibers that ferry signals toward the cell body dendrites.) Today, more and more is being learned about them. Neurons are not all alike in the way they look or function. In fact, they differ from one another more than cells in any other organ. The brain is a multi-diverse and inclusive universe. (Source)

Each endogenous neurotransmitter has a matching receptor molecule, and they function like a lock and a key. There must be a matching receptor for the brain chemical. If there is no matching receptor then the neurotransmitter cannot influence the cell. (Herrmann, Ned. The Whole Brain Business Book. p 216. NY: McGraw-Hill, 1996.)

The hippocampus has the highest concentration of LTP neurons in the brain. Some may stay on for only a couple of seconds, others for a few days or months. This may be the reason that you may have difficulty getting rid of specific emotional feelings long after the event that triggered them is over. (Giuffre, Kenneth, MD. The Care and Feeding of Your Brain. p 48-52. NJ: Career Press, 1999.)

Rather than memories being bottled up inside neurons, they appear to be stored in the connections between neurons, in the spaces between them—the synapses. (Fields, R. Douglas, PhD. Pg 22. NY: Simon & Schuster, 2010)

Individual memories are burned onto hundreds of receptors that are constantly in motion around nerve synapses. Some escape. A specific set of molecules catch these elusive receptors and take them to a recycling plant where they are reprocessed and returned to the synapse intact. (Duke University Medical Center (2007, September 24. New Understanding of Basic Units Of Memory. Science Daily.)

Messages are sent across the synaptic cleft by means of chemical substances known as neurotransmitters. Synaptic vesicles (microscopic “bottles” inside neurons) filled with neurotransmitters are visible only under the high-power magnification of an electron microscope. The force of an electrical impulse smashes one or more bottles against the cell wall, releasing the contents into the synaptic gulf. The chemicals then diffuse across to the opposite shore. (Fields, R. Douglas, PhD. The Other Brain. p 19-21. NY: Simon & Schuster, 2009.)

Metachromatic Leukodystrophy, caused by an enzyme deficiency that allows sulfatides to accumulate in the nervous sytem and damage the myelin sheath, is a slowly progressive genetic disorder. Symptoms may appear during the first four years of life for late infantile MLD, between ages 6 and 16 for late-stage juvenile MLD, and after age 16 for adult disease. Symptoms may include decline in school or work performance, loss of metnal functions and muscle control, behavioral problems, and seizures. (U.S. National Library of Medicine. Metchromatic Leukodystrophy. Accessed 2007.)

Once a neuron is born it has to travel to the place in the brain where it will do its work. Scientists have seen that neurons use at least two different methods to travel:

Some neurons migrate by following the long fibers of cells called radial glia. These fibers extend from the inner layers to the outer layers of the brain. Neurons glide along the fibers until they reach their destination.

Neurons also travel by using chemical signals. Scientists have found special molecules on the surface of neurons—adhesion molecules—that bind with similar molecules on nearby glial cells or nerve axons. These chemical signals guide the neuron to its final location.

Not all neurons are successful in their journey. Scientists think that only a third reach their destination. The rest either never differentiate, or die and disappear at some point during the two to three week phase of migration. Some neurons survive the trip, but end up where they shouldn’t be. Mutations in the genes that control migration create areas of misplaced or oddly formed neurons that can cause disorders such as childhood epilepsy or mental retardation. Some researchers suspect that schizophrenia and the learning disorder dyslexia are partly the result of misguided neurons. (National Institutes of Health. National Institute of Neurological Disorders and Strokes. Accessed 2010)

During gestation neurons migrate to various regions of the brain. Proper migration is important for the development of normal brain function. There is a lengthening list of disorders, including autism, dyslexia, epilepsy, and schizophrenia that may be caused in part by migration problems. (Ratey, John J., MD. A User’s Guide to the Brain. p 23. NY: Vintage Books, 2002.)

Errors in migration of neurons can show up later in conditions such as epilepsy, dyslexia, and perhaps schizophrenia. (Wolfe, Patricia, PhD. Brain Matters. p 18-20. Virginia: ASCD, 2001.)

Dr. Daniel Siegel is the founder of interpersonal neurobiology, a new field that studies the "social brain." The social brain includes a multitude of circuitry designed to interact with another person's brain. One key discovery was "mirror neurons." They activate in your brain what you see in another person, including emotions, movements, and even intentions. Studies by neuroscientist Tania Singer showed women tend to be more highly developed in the mirror neuron system, and so rely on it more than men do for signals of empathy. Men tend to have a burst of the mirror neuron system and then go into a problem-solving mode. (Goleman, Daniel Jay, PhD. The Brain and Emotional Intelligence: New Insights. p 54-65. MA: More Than Sound, 2011)

Mirror neurons are brain cells that form an important part of your "mind's body." (You also have a mind's eye and a mind's ear). They help you understand the actions and intentions of others. When someone reaches for a glass of water, your mirror neurons do the same thing in your mind's body. Some of the same neurons that are active when you take a drink, are active when you think someone you can see is about to take a drink. Your brain makes a prediction (e.g., person is thirsty and will raise glass to lips and take a drink). It also runs a simulation, autmatically and subsoncsiously. (Macknik, Stephen L. PhD and Susana Martinez-Conde PhD. Sleights of Mind. p 69-72. NY: Henry Holt and Company, 2010.)

Mirror neurons play a key role in sexual response and may play a role in homophobia. When people see sexually aroused genitals of thepreferred sex (e.g., opposite for heterosexuals, same for homosexuals), the brain's mirror neurons and reward centers fire. So when a heterosexual male sees two other men in sexual acts, he can't help but experience it in his mind's body, even if it is at a subconscious level. For the straight male, this is unappetizing and may make a live-and-let-live attitude more difficult to adopt. (Blakeslee, Sandra, and Matthew Blakeslee. The Body Has a Mind of Its Own. p 178-179. NY: Random House, 2008.)

During the second half of their first year of life, infants showed pro-active directed eye movements that seem to require observing the hand of an agent and an object, supporting the mirror neuron account in general. Infants develop this gaze behavior during the very limited time frame derived from the MSN hypothesis of social recognition. During this time period, infants come to predict others’ actions. The mirror neuron system is likely to predict this process. (Falck-Ytter, Terje, et al. Infants predict other people's action goals, Nature Neuroscience 9, 2006)

Abstract: In the ventral premotor cortex (area F5) of the monkey there are neurons that discharge both when the monkey performs specific motor actions and when it observes another individual performing a similar action (mirror neurons). Previous studies on mirror neurons concerned hand actions. Here, we describe the mirror responses of F5 neurons that motorically code mouth actions. The results showed that about one-third of mouth motor neurons also discharge when the monkey observes another individual performing mouth actions. The majority of these ‘mouth mirror neurons’ become active during the execution and observation of mouth actions related to ingestive functions such as grasping, sucking or breaking food. Another population of mouth mirror neurons also discharges during the execution of ingestive actions, but the most effective visual stimuli in triggering them are communicative mouth gestures (e.g. lip smacking). Some also fire when the monkey makes communicative gestures. These findings extend the notion of mirror system from hand to mouth action and suggest that area F5, the area considered to be the homologue of human Broca’s area, is also involved in communicative functions. [Accessed Mar 2015. http://www.uni-muenster.de/imperia/md/content/psyifp/aeechterhoff/wintersemester2011-12/vorlesungkommperskonflikt/ferrari_mirrorneuronsmonkey_eurjourneuro_2003.pdf]

One recent discovery that has been made by researchers in Italy, in Parma, by Giacomo Rizzolatti and his colleagues, is a group of neurons called mirror neurons, which are on the front of the brain in the frontal lobes. But what Rizzolatti found was a subset of these neurons, maybe about 20 percent of them, will also firewhen I'm looking at somebody else performing the same action. So, here is a neuron that fires when I reach and grab something, but it also fires when I watch Joe reaching and grabbing something. And this is truly astonishing. Because it's as though this neuron is adopting the other person's point of view. It's almost as though it's performing a virtual reality simulation of the other person's action. [Accessed Mar 2015. http://www.ted.com/talks/vs_ramachandran_the_neurons_that_shaped_civilization/transcript?language=en]

Mirror neurons are a type of brain cell that respond equally when we perform an action and when we witness someone else perform the same action. They were first discovered in the early 1990s, when a team of Italian researchers found individual neurons in the brains of macaque monkeys that fired both when the monkeys grabbed an object and also when the monkeys watched another primate grab the same object.

Neuroscientist Giacomo Rizzolatti, MD, who with his colleagues at the University of Parma first identified mirror neurons, says that the neurons could help explain how and why we "read" other people's minds and feel empathy for them. If watching an action and performing that action can activate the same parts of the brain in monkeys--down to a single neuron--then it makes sense that watching an action and performing an action could also elicit the same feelings in people. [Accessed Mar 2015. http://www.apa.org/monitor/oct05/mirror.aspx]

Subsequent research on both monkeys and humans, is that in a healthy premotor cortex, the difference is about 80 percent. In other words, about one-fifth of the neurons that fire in the premotor cortex when we perform an action (say, kicking a ball) also fire at the sight of somebody else performing that action. A smaller percentage fire even when we only hear a sound associated with an action (say, the crack of a bat). This subset of motor neurons that respond to others’ actions as if they were our own are called “mirror neurons,” and they seem to encode a complete archive of all the muscle movements we learn to execute over the course of our lives, from the first smile and finger wag to a flawless triple toe loop. [Accessed Mar 2015. http://grantland.com/features/this-your-brain-sports/]

Resources for further information on the science behind mirror neurons:

Some neurons fire in response to simultaneously occurring sights and sounds, sounds and touches, sight and touches, and so on. They are found throughout the cortex and in the superior colliculus (midbrain region densely packed with multisensory neurons). (Macknik, Stephen L. PhD and Susana Martinez-Conde PhD. Sleights of Mind. p 116-120. NY: Henry Holt and Company, 2010.)

Researchers at Stanford University have found that proficient reading requires efficient communication between brain areas that involve vision, hearing, and language. These areas are distributed throughout the brain so the development of reading ability relates to growth in the brain’s white-matter tracts, bundles of myelinated nerve fibers that connect these distant regions of the brain. The growth of these white-matter tracts is governed by pruning (the elimination of extraneous nerve fibers and neuronal connections); and myelination (the coating of nerve fibers with myelin, a fatty, insulating tissue that increases the speed of transmission). Both processes are influenced by experience: underused nerve fibers are pruned while others are myelinated--so they occur at different rates and times in different people. Bottom line? Read to children; listen to them read. Read aloud to yourself. Keep those nerve fibers stimulated! (Source)

Myelin is the insulation that must be laid down on the axons of neurons to allow signals to pass efficiently along them. (Carter, Rita, Ed. Mapping the Mind. p 20. CA: University of California Press, 1998.)

The myelin sheath allows signals to pass along the axons of neurons 100 times faster than they could without the coating. Myelination occurs at different times in brain development. Some neurons never develop a myelin coat. (Zull, James, E., PhD. The Art of Changing the Brain. p 162-164. Virginia: Stylus Publishing, LLC, 2002.)

Myelin is produced by two types of neuroglia: Schwann cells in the peripheral nervous system (neurolemma may help regeneration post injury) and Oligodendrocytes in the central nervous sytem (no neurolemma present). The amount increases from birth to maturity. Myelin increases speed of nerve impulse conduction. (Tortora, Gerard J., and Sandra R. Grabowski. Principles of Anatomy and Physiology, 10th Edition. p p 292-293. NY: John Wiley & Sons, Inc., 2003.)

Myelin is a lipid and protein covering for the axons of most neurons, produce by neuroglia. This sheath insulates the axon and increases the speed of nerve impulse conduction. The amount increases from birth to maturity. (Tortora, Gerard J., and Sandra R. Grabowski. Principles of Anatomy and Physiology. p 392-393. NY: John Wiley & Sons, Inc., 2003.)

An insulating layer known as the myelin sheath wraps the axon throughout its length, helping it conduct electrical signals from the skin to the spinal cord at up to 425 feet per second. From there, signals are relayed to the brain stem, then to the thalamus, and then to the cerebrum’s sensory cortex. (Restak, Richard.Mysteries of the Mind. p 14. Washington, DC: National Geographic, 2000.)

Diffusion-Tensor Imaging or DTI, a variation of magnetic resonance imaging, is able to measure the diffusion of water molecules through tissue. In studies of 92 pairs of fraternal and identical twins, researchers found a strong correlation between the integrity of the white matter (e.g., myelin that coats neuronal axons) and performance on a standard IQ test. A high quality of myelin (that seems to be inheritable) appears to correlate with higher IQ scores. (Singer, Emily. Brain Images Reveal the Secret to Higher IQ. Technology, 2009.)

The development of myelin in the spine proceeds from top to bottom. Mouth, eyes, arms, and hands are use adeptly before legs and feet. (Healy, Jane M., PhD. Your Child’s Growing Mind. p 31-32, NY: Doubleday, 1987.)

Myelin is the insulation that must be laid down on the axons to allow signals to pass efficiently along them. At birth many of the axons on the 100 billion neurons are as yet unmyelinated. Myelinization begins in prefrontal lobes about the time language areas become active. (Carter, Rita, Ed. Mapping the Mind. p 20. CA: University of California Press, 1998.)

Myelin is a substance that insulates the wiring of the brain and facilitates clear, rapid transmission of information. Myelination is not completed until the twenties or longer. (Healy, Jane M., PhD. Endangered Minds. p 66-70. NY: Simon & Schuster, 1990.)

The development of myelin around the axons likely accounts largely for the tripling of brain weight after birth. (Diamond, Marian, PhD, and Janet Hopson.Magic Trees of the Mind. p 48-49. NY: Dutton, 1998.)

The myelin sheath allows signals to pass along the axons 100 times faster than they could without the coating. Myelination occurs at different times in brain development. Some neurons never develop a myelin coat. (Zull, James, E., PhD.The Art of Changing the Brain. p 162-164. Virginia: Stylus Publishing, LLC, 2002.)

Girls’ brains mature earlier than boys’. Myelination continues in all brains into the early twenties, but in young women it is complete earlier than in young men. (Gurian, Michael, PhD, and Patricia Henley, with Terry Trueman. Boys and Girls Learn Differently! p 18-26. CA: Jossey-Bass, 2001.)

Myelination in the spine occurs from top to bottom. Therefore, it is completed in the mouth, hand, and arms, before it is adequately completed in the legs and feet. (Healy, Jane M., PhD. Your Child’s Growing Mind. p 31-32. NY: Doubleday, 1987, 1989.)

The final layer of myelin is not completed until the mid-twenties.(Greenfield, Susan, Con. Ed. Brain Power. p 157. Britain: Element Books Limited, 1999.)

The reticular formation (e.g., maintaining attention), usually only becomes fully myelinated at or after puberty, which is why prepubescent children have a short attention span. The frontal lobes do not become fully myelinated until full adulthood. (Carter, Rita, Ed. Mapping the Mind. p 20. CA: University of California Press, 1998.)

As with our muscles, we can strength our neural pathways with brain exercise. Or we can let them wither. The principle is the same: use it or lose it! (Ratey, John J., MD. A User’s Guide to the Brain. p 47. NY: Vintage Books, 2002.)

Although the brain is thought of primarily as an organ of the nervous system, it can also act as an endocrine gland through its production of hormones called neurohormones (e.g., oxytocin is produced in the brain and then travels to the pituitary where it is secreted into the blood). (Arnold, Caroline. Sex Hormones - why males and females are different. p 29. NY: William Morrow & Company, 1981. )

Mature neurons don’t undergo cell division so rarely become cancerous (e.g., cancer is a failure of brakes that stop cellular division thus leading to runaway growth of cells into tumors). Neuroblastomas do occur although they are not common. They usually arise in the first three years of life and are rarely seen in adults. (Fields, R. Douglas, PhD. The Other Brain. p 74-75. NY: Simon & Schuster, 2009.)

The term neurogenesis refers to the creation of new neurons. (LeDoux, Joseph.Synaptic Self. p 66-68. NY: Penguin Books, 2002.)

Neurogenesis increases our understanding of neuroplasticity, the brain's ability to reshape itself. Every day the brain has been found to generate 10,000 stem cells that split into two: one becomes a line that continues to make stem cells; the other goes to wherever it is needed in teh brain and becomes the type of cell that is needed. (Source)

In the first month after conception, the human brain begins to develop. Approximately 250,000 neurons are generated each minute, so within six months most of the billions of neurons have been created. Shortly after their creation, neurons become differentiated, assume specialized roles, migrate to their assigned position, and form synapses so they can store information and communicate with each other. (Schramm, Derek D., PhD. The Creative Brain. p 2. CA: Institute for Natural Resources, Health Update. 2007.)

Because of its plasticity throughout life, the brain can rewire itself in response to new learning, and can even create new cells (neurogenesis) under specific circumstances. (On the Brain, newsletter. p 2-3. CA: 2005.)

Research 1998, Eriksson: in adulthood the brain can grow new neurons, at least in the hippocampus. (Jensen, Eric. Brain-Based Learning (Revised). p 28. CA: The Brain Store, 2005.)

In Fragile X, Downs, and perhaps in Autism, the genetics differ but the end result for the brains appear to be similar. The gene Fmr1 located on the X chromosome, influences neurons to be less likely than normal cells to reach out and form connections, or synapses, with their neighbors. Fewer cells are making connections. (Medicine and Science. Fragile X, Down syndromes linked to faulty brain communication.)

Using a new technique to count neurons, Frederico Azevedo and colleagues found that the adult male brain contains on average 86 billion neurons and 85 billion nonneuronal cells. Although the cerebral cortex is 82% of the brain's mass, it possesses only 19% of the brain's neurons (about 17 billion). The majority, 69 billion or 72% of neurons, were found in the crebellum, which makes up 10% of the brain's mass. The rest of the brain has about one billion neurons. (Gazzaniga, Michael S.Who's In Charge? p 30-32. NY: HarperCollins Publishers, 2009)

The vast network of the human brain contains two-hundred billion neural cells, each connected with anywhere from 1,000 to 10,000 other cells. This creates the potential for any neuron to influence a distant other neurons via any number of intervening connections. (Restak, Richard, MD. The Brain has a Mind of its Own. p 36-40. NY:Crown Publishers, Inc. 1991.)

Neurons are the most fundamental signaling units of the human nervous system. They gather information about the brain’s internal state and the body’s external environment, analyze the data, and respond by coordinating appropriate actions. Typically neurons consists of:

Cell body or soma (metabolic center and primary site of neuronal protein synthesis)

Dendrites (the primary conduits for receiving information from other neurons)

Axons (may be more than 3 feet long and emit neurotransmitters that transport messages from one cell to another)

Presynaptic terminals (numerous delicate swellings at the end of an axon that end at a synapse)

At birth the brain has about 100 billion neurons. They way they are connected determines a person’s mental characteristics. Each neuron is connected to hundreds of other neurons by anywhere from 1000 to 10,000 synapses. Edelman (1992) estimates that it would take some 32 million years to count synapses in the cerebral cortex alone. (Howard, Pierce J., PhD. The Owner’s Manual for the Brain. p 44-45. GA:Bard Press, 1994, 2000.)

At birth the brain contains as many neurons–about 100 billion–as it will have as an adult. The neurons are immature, connections between them are sparse, and many of their axons are as yet not myelinated. (Carter, Rita, Ed. Mapping the Mind. p 20. CA: University of California Press, 1998.)

There are estimated to be about 100 billion neurons in the brain give or take a few billion. Most neurons have one main axon and as many as 100,000 dendrites (or finger-like projections). Axons and dendrites, and their connections, can be modified up to a point, strengthened, and perhaps even re-grown. (Ratey, John J., MD. A User’s Guide to the Brain. p 19-20. NY: Vintage Books, 2002.)

Wilhelm Waldeyer published a paper in 1891 in which he suggested that brain cells be called neurons. (LeDoux, Joseph. Synaptic Self. p 37. NY: Penguin Books, 2002.)

Each neuron in the human brain makes an average 1,000 or so connections with other neurons. There are 100 billion neurons, so the brain probably contains 100 trillion synapses, its most critical working part. (Wade, Nicholas. In Map of Brain Junction, Avenues to Answers. (Source)

You can define neurons as part of the brain, but neurons end up on organs. The whole GI tract, for example, has its own built-in nervous system. You can get stomach pains when you are nervous. (Giuffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. p 12. NJ: Career Press, 1999.)

It is estimated that the brain contains one hundred billion neurons, each with an average of 10,000 connections to other neurons. Collectively, they are over two million miles long. (Siegle, Daniel J., MD. The Developing Mind. p 11-13. NY: The Guilford Press, 1999.)

Each neuron grows a single axon (send) and many dendrites (receive) that divide at hundreds of branch points. There may be 50 different types of neurons in the brain. (Schwartz, Jeffrey M., MD, and Sharon Begley. The Mind & the Brain. p 102-106. NY: Regan Books, 2002.)

The cells that actually craet brain activity—about one in ten of the total—are neurons, cells that are adapted to carry an electrical signal from one to another. (Carter, Rita, Ed. Mapping the Mind. p 14. CA: University of California Press, 1998.)

Neurons appear to be little “brains” in their own right. The most powerful computer does not have the information-processing skill of a single neuron. There are different types of neurons. Some respond specifically to one thing (e.g., an edge, a narrow range of light waves). Others combine information into complex representations. (Carter, Rita, Ed. Exploring Consciousness. p 118. CA: University of California Press, 1998.)

For experience to alter the brain the neurons themselves must be altered. (Ornstein, Robert, PhD. The Roots of the Self. p 183. NY: HarperCollins Publishing, 1995.)

It is estimated that the human brain contains 100 billion or more neurons and many times as many supporting cells. Its outer surface, the cerebral cortex, alone contains 30 billion neurons. (Restak, Richard. Mysteries of the Mind. p 11-12, 20-21. Washington, DC: National Geographic, 2000.)

In 1998 a team of American and Swedish scientists demonstrated for the first time that new brain cells are generated in adult humans. In addition, old neurons can grow dendrites to compensate for losses. (Katz, Lawrence C., PhD and Manning Rubin. Keep Your Brain Alive. p 3. NY: Workman Publishing Company, Inc., 1999.)

There are as many neurons and glial (supporting) cells as there are stars in the Milky Way. (Brynie, Faith Hickman. 101 Questions Your Brain Has Asked About Itself But Couldn’t Answer, Until Now. p 11, 32, 41. CT: Millbrook Press, 1998.)

The brain contains approximately 10 billion neurons, each capable of making 1000 synaptic connections. In the human brain there are about 10 trillion synapses. (Fisher, Helen, PhD. Why We Love. p 68-69. NY: Henry Holt and Company, 2004.)

Neuron proliferation begins within the first 4 weeks of development and is complete by 24 weeks. The process of neuronal migration to their intended location in the brain begins at about the same time and tapers off by about the 30th week. (Karr-Morse, Robin, and Meredith S. Wiley. Ghosts from the Nursery. p 52-53. NY:Atlantic Monthly Press, 1997.)

During gestation, the neurons migrate to various regions of the brain. There is a lengthening list of disorders, including autism, dyslexia, epilepsy, and schizophrenia that may be caused in part by a migration problem. (Ratey, John J., MD. A User’s Guide to the Brain. p 23. NY: Vintage Books, 2002.)

Most of a person’s neurons are formed during gestation. At some stages nerve cell division is so rapid that 250,000 new neurons form every minute. Before birth the brain grows to 2/3rd of its adult size, but only about 10% of its eventual weight. (Brynie, Faith Hickman. 101 Questions Your Brain Has Asked About Itself But Couldn’t Answer, Until Now. p 17-26. CT: Millbrook Press, 1998.)

At peak production about 250,000 neurons are being generated per minute (neurogenesis). Synaptogenesis (the creation of new synapses between existing neurons) probably occurs up until the moment of death. (LeDoux, Joseph. Synaptic Self. p 66-68. NY: Penguin Books, 2002.)

About 250,000 new neurons are generated each minute during the peak of cell proliferation during gestation. (Restak, Richard, MD. The Secret Life of the Brain. p 8. Washington D.C.: The Dana Press and Joseph Henry Press, 2001.)

When released in the brain, neuropeptide Y reduces anxiety and depression and can improve memory. It has the opposite effect of Substance P. (Perricone, Nicholas, MD. The Perricone Promise. p 28-30. NY: Warner Books, 2004.)

Peptides are molecules consisting of 2 or more amino acids. Peptides are smaller than proteins, which are also chains of amino acids. The dividing line is at about 50 amino acids. Depending on the number of amino acids, peptides are called dipeptides, tripeptides, tetrapeptides, and so on. (They appear able to impact one's mood. (Source)

Neuropeptides are tiny chains of amino acids that are involved with one’s emotional experiences; bits of brain that float all over the body. (Pearsall, Paul, PhD. The Heart’s Code. p 10. NY: Broadway Books, 1998.)

In addition to electrical signaling, the heart releases peptides that can impact your mood. Think of the heart as an endocrine gland. The peptides it releases help in blood pressure modulation and improving the functioning of kidneys. These peptides also stimulate the pituitary gland thereby helping it to release hormones like oxytocin commonly referred to as “love” or bonding hormone. Oxytocin also helps in increasing a sense of wellbeing. This could be a basis for saying that happy feelings emanate from the heart. (Cartin, M., and J. Genest. The Heart as an Endocrine Gland. Scientific American, February 1986, Vol. 254, No. 2, p 62-67)

Neuropeptides are messengers (nature’s cell phones). Along with hormones and neurotransmitters, they control every aspect of brain and body. They can be released in the brain from touch receptors in the skin. (Perricone, Nicholas, MD. The Perricone Promise. p 6-8. NY: Warner Books, 2004.)

Peptides (composed of many amino acids) are a class of slow-acting modulatory substances found throughout the brain. Neuroactive peptides act in the nervous system. The best known of these are the opiates: endorphins and enkephalins. (LeDoux, Joseph. Synaptic Self. p 57-58. NY: Penguin Books, 2002.)

Neuropil is the name of the space between cell bodies. It is filled with axons, dendrites, and synapsez. In general, the larger the area, the better connecgted it is. Not every neuron is connected to every other neuron, however. (Gazzaniga, Michael S. Who's In Charge? p 32-34. NY: HarperCollins Publishers, 2009)

Social interactions play a role through neuroplasticity. Repeated experiences reshape the brain in terms of size, shape, and number of neurons and their synaptic connections. Our relationships have subtle, yet powerful, lifelong impacts upon us. (Goleman, Daniel, PhD. Social Intelligence. p 11. NY: Bantam Dell. 2006.)

Several dozen neurotransmitters have been identified. Some like GABA are found everywhere in the brain. Others like dopamine are restricted to certain regions. Each neurotransmitter can bind to several receptor types some of which are ubiquitous and others region-specific. (Goldberg, Elkhonon. The Executive Brain. p 28. NY: Oxford University Press. 2001.)

Strong emotional stimuli release hormones and neurotransmitters that help to embed that emotional memory in your neural circuitry. You tend to remember things in relation to how important they are to you and are more likely to recall strong negative emotional states than positive ones. (Childre, Doc and Howard Martin. The HeartMath Solution. p 202-203. CA: Harper SF, 1999.)

Nerve Growth Factor (NGF) was the first neurotrophin discovered, almost 50 years ago, at Washington University in St. Louis. It was found to not only keep certain types of nerve cells alive but cause them to sprout new branches. (Katz, Lawrence C., PhD and Manning Rubin. Keep Your Brain Alive. p 141. NY: Workman Publishing Company, Inc., 1999.

Neurotrophins are an important set of molecules, brain food, that stimulate active neuron terminals to sprout new synaptic connections. Only those cells that compete successfully for neurotrophins (those that are active) survive. (LeDoux, Joseph.Synaptic Self, How Our Brains Become Who We Are. p 81-82. Penguin Books 2002.)

The human brain can create new neural tissue as well as new neural connections and pathways throughout adulthood. (Goleman, Daniel, PhD, with Richard Boyatzis, and Annie Mckee. Primal Leadership. p 102-104. Boston: Harvard Business School Press, 2002.)

Related to adrenaline (epinephrine), norepinephrine is a neurotransmitter absolutely vital to the booting-up process. It activates cortex neurons in a state of “readiness,” while at the same time directing blood flow to areas that need it. (Guiffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. p 30-32. NJ: Career Press, 1999.)

A derivative of dopamine, norepinephrine can contribute to a “lover’s high,” although effects vary depending on the brain section activated. Outcomes can include: loss of appetite, sleeplessness, ecstasy, and increased energy. It can also increase testosterone levels. (Fisher, Helen, PhD. Why We Love. p 52-60. NY: Henry Holt and Company, 2004.)

Studies: Alterations of norepinephrine and other neurotransmitters may affect the creative process. The minds of exceptionally creative people may be capable of regulating norepinephrine – to decrease levels during periods of creative innovation and pave the way for discovery of unanticipated associations. High levels of norepinephrine constrict the diversity of available concepts; low levels have the opposite effect. (Heilman, K. M. Creative Innovation: Possible Brain Mechanisms.9(5):369-379. Neurocase. 2003.)

Studies: Alterations of norepinephrine and other neurotransmitters may affect the creative process. The minds of exceptionally creative people may be capable of regulating norepinephrine – to decrease levels during periods of creative innovation and pave the way for discovery of unanticipated associations. High levels of norepinephrine constrict the diversity of available concepts; low levels have the opposite effect. (Heilman, K. M. Creative Innovation: Possible Brain Mechanisms.9(5):369-379. Neurocase. 2003.)

Baby monkeys whose mothers are exposed to a major stress while pregnant show the signs of that stress in their temperament, displaying an inhibited temperament reflected in their altered levels of noradrenaline and dopamine. (Quartz, Steven R., PhD, and Terrence J. Sejnowski PhD. Liars, Lovers, and Heroes. p 126. NY: HarperCollins Publishers Inc., 2002.)

The video-based spinning woman illusion has been making the rounds on the internet. Olivia Carter, a neuroscientist at the University of Melbourne in Australia, and her team, found that people's pupils dilate when they switch between two alternative ways of viewing an optical illusion (e.g., the woman seems to switch direction but in fact does not). The effect results from the viewer swapping how they view her. Eye pupils dilate in stressful situations as part of the "fight-or-flight" response. The reflex is mediated by the release of the hormone noradrenalin. Noradrenalin helps you to cement decisions toward which you are moving. Pupil dilation is an outward sign of this. (Source)

Olfactory receptor cells, neurons in your nose that allow you to smell (to detect odors), regenerate throughout life. Although these cells are continually being born and dying, they maintain the same connections as their ancestors. The result is that once you learn a smell (an odor), it always smells the same to you – despite the fact that there are always new neurons smelling it! (Brain Facts.)

Human brain contains about as many neurons as there are starts in the Milky Way (e.g., 100 billion), and 100 trillion glial cells. (Gurian, Michael, PhD, and Patricia Henley, with Terry Trueman. Boys and Girls Learn Differently! p 17-20. CA: Jossey-Bass, 2001.)

The brain has over 100 billion neurons. (Newberg, Andrew, MD., and Mark Robert Waldman. Why We Believe What We Believe. p 17-20. NY: Free Press, 2006.)

The brain has about 100 billion neurons. By comparison: a monkey has 10 billion, a mouse has 5 million, and a fruit fly has 100,000. (Jensen, Eric. Brain-Based Learning (Revised). p 11. CA: The Brain Store, 2005.)

We have roughly 86 billion neurons in our brains.But unlike the common saying, we don’t just use 10% of them; we use most of them all of the time!

When you watch two people who are in tune with each other, they often exhibit similar movements. The movements are orchestgratged by neurons known as oscillators. They regulate how one person's body moves in relationship to another body. (Port, R., and T. Van Gelder. Mind as Motion: Explorations in the Dynamics of Cognition. MA: MIT Press, 1995)

Pain fibers are not insulated with myelin. Impulses travel through pain fiber axons at the rate of 2 miles per hour (ab out the pace of your footsteps in a slow walk). This explains the build-up to full painful sensations when you accidentally hit your thumb with a hammer. (Fields, R. Douglas, PhD. The Other Brain. p 19. NY: Simon & Schuster, 2009.)

Most of the neurons you will ever have are in your brain at birth. The patterns in which neurons connect to each other, however, develop and change throughout life. (Childre, Doc and Howard Martin. The HeartMath Solution. p 26. CA: Harper SF, 1999.)

Pelizaeus-Merzbacher Disease is caused by mutation in a gene that regulates production of myelin protein. It is a rare, degenerative disorder of the Central nervous system. Onset may occur in infancy and often results in death in early childhood. The milder, adult-onset form of PMD often involves spastic paraplegia. (National Institute of Neurological Disorders and Stroke. NINDS Pelizaeus-Merzbacher Disease Information Page. Accessed 2007.)

The maintenance of neuronal connections is an active process that requires constant repression of the formation of nerve sprouts by the protein calpain to avoid uncontrolled growth. But a consequence of this role is that calpain limits neural plasticity and the brain’s ability to repair itself. The next step is to find a way to enhance neural plasticity without interfering with the good connections that are already in place. (New Discovery Could Rejuvenate the Brain. 2008.)

Progressive Multifocal Leukoencephalopathy is caused by a reaction to a common virus that destroys white matter, a component of myelin. This rare disease may occur in people who have AIDS or who have had an organ transplant, in recipients of immunosuppressive therapy, or in the presence of conditions such as Hodgkins’s disease, lymphoma, sarcoidosis. (National Institute of Neurological Disorders and Stroke. NINDS Progressive Multifocal Leukoencephalopathy Disease Information Page. Accessed 2007.)

Reported in March 23, 2000 issues of “Science:” The strengthening of nerve cell connections in the brain, believed to occur during learning and memory consolidation, can be largely explained by the movement of proteins called AMPA receptors into synapses. (Cold Spring Harbor Laboratory (2000, March 28. New Link Uncovered In Nerve Cell Mechanism Thought (To Power Learning And Memory. Science Daily.)

Each neurotransmitter must have a matching receptor that functions much like a lock and a key. If there is no matching receptor, neuron-to-neuron synapse will not take place. (Herrmann, Ned. The Whole Brain Business Book. p 216. NY:McGraw-Hill, 1996.)

The majority of neurons (as compared with holistic thinking) appear to reduce and categorize one’s experience. The left hemisphere appears to carry out primarily reductionist thinking. The human brain is capable of both holistic and reductionist thinking but not at the same time. (Newberg, Andrew, MD and Mark Robert Waldman. Why We Believe What We Believe. P 92-94. NY: Free Press, 2006)

There are high numbers of serotonin receptors in the intestines. Because of this when these receptors get flooded with excess serotonin (e.g., Prozac) the individuals may experience G.I. disorders. This may also happen to cells in the immune system that have similar receptors on their surfaces. (Pert, Candace, PhD. Molecules of Emotion. p 267. NY: Scribner, 1997.)

Serotonin and Dopamine must be constantly rebalanced in the brain. Stress can negatively impact this balance. When the rebalancing efficiency is impacted seriously, the chemical balance become severe enough to begin to see symptoms (e.g., depression). (Bost, Brent W., MD, FACOG. Hurried Woman Syndrome. p 14-15. NY: Vantage Press, 2001.)

Dieting starves the brain of serotonin. This can trigger a cycle of dieting and bingeing, as there isn’t enough serotonin to signal satisfaction. (Brynie, Faith Hickman. 101 Questions Your Brain Has Asked About Itself But Couldn’t Answer, Until Now. p 38-43. CT: Millbrook Press, 1998.)

Serotonin is manufactured in the body from trypotphan, found in food high in carbohydrates (cereals). Serotonin can sexually stimulate females but apparently not males. (Durden-Smith, Jo, and Diane deSimone. Sex and the Brain. p 254-260. NY: Arbor House Publishing, 1983.)

Cells in the brainstem (raphe nuclei) produce serotonin and their projections carry it to all parts of the brain. Too much serotonin results in everything from sleepiness to fatigue; to little serotonin is associated with states of anger, aggression, anxiety, and depression. (Guiffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. NJ: Career Press, 1999.)

Studies using PET scans: males produce serotonin at a rate that is 52% higher than that produced by females. (Howard, Pierce J., PhD. The Owner’s Manual for the Brain. p 15, 334. GA: Bard Press, 1994, 2000.)

Elevated levels of dopamine and norepinephrine have been associated with decreased levels of serotonin. This, in turn, is associated with persistent thoughts about the other individual. (Fisher, Helen, PhD. Why We Love. NY: Henry Holt and Company, 2004.)

Serotonin can help you slow down and fall asleep. It is made in the brain with tryptophan, an amino acid. (There is no tryptophan in the carbohydrates themselves.) (Bricklin, Mark, et al. Positive Living and Health. p 91-92. PA:Rodale Press, 1990.)

Research shows that being on the receiving end of an act of kindness actually increases your serotonin levels substantially thus giving you a natural boost of the "feel goods." The great news about giving the gift of kindness to someone is that it's not only the receiver who benefits but also the person who delivers the act of kindness, almost equally. And it doesn't stop there. Anyone who witnesses the act or later hears about it also benefits from elevated levels of serotonin. (Source)

Serotonin is a naturally occurring substance in the brain and body. It helps you to feel peaceful and more comfortable. Studies have shown that a simple act of kindness directed toward another improves function of the immune system and stimulates the production of serotonin in both the person who did the act of kindness and in the recipient. Persons overseeing the act of kindness experience similar beneficial results. (Dyer, Wayne, PhD. The Power of Intention. p. 25-26. CA: Hay House, Inc, 2004)